1. Field of the Invention
The present invention relates generally to connectors, and more particularly to a connector having a circuit element built therein.
2. Description of the Related Art
Vehicular AC (alternating current) generators have a connector for communication of signals with external electronic control units (ECUs). Typical examples of such vehicular AC generators are disclosed in Japanese Patent Laid-open Publications (JP-A) Nos. 2001-016829 (corresponding to U.S. Pat. No. 6,291,913 B1) and 2002-033438 (corresponding to U.S. Pat. No. 6,390,854 B2). It has been a conventional practice that a circuit element such as surge absorber is incorporated or built in the connector. Such connector having a circuit element built therein will be hereinafter referred to as “connector with a built-in circuit element”. The circuit element to be built in the connector may include capacitors, resistance elements, varistors, various passive or active elements, and ICs. For these circuit elements, leaded circuit elements, which do not need a circuit board, are employed. The leaded circuit elements each have leads extending in a longitudinal direction from opposite ends thereof.
One example of such conventional connectors with a built-in circuit, which is employed in a vehicular AC generator, will be described with reference to FIGS. 7 to 9. FIG. 7 is a front elevational view of the connector, FIG. 8 is a rear elevational view of the connector, and FIG. 9 is a vertical cross-sectional view of the connector with sealing resin filled therein.
In FIGS. 7-9, reference numeral 100 denotes a connector case as a resin molded article, 102 to 105, wiring metal pieces fixed or embedded in the connector case 100 by insert molding or resin molding; and 106, a leaded circuit element. The connector case 100 includes a body portion 112 of rectangular block-like configuration having laterally-elongated element accommodating chambers 111a and 111b, and a tubular connector portion 113 projecting from the body portion 112 in an upward direction in FIGS. 7-9 The leaded circuit element 106 has an element body 160 and a pair of leads 161 and 162 extending from opposite ends of the element body 160 in a longitudinal direction thereof The leaded circuit element 106 solely or in combination with another circuit element offers the function of a surge absorbing circuit such as snubber circuit. A tip of the lead 161 is soldered to an element-connecting terminal 132 of the wiring metal piece 103, and a tip of the lead 162 is soldered to an element-connecting terminal 152 of the wiring metal piece 105. Numeral 200 shown in FIG. 9 denotes a partition wall provided in the connector case 100 to isolate the element accommodating chamber 111a on the front side from the element accommodating chamber 111b on the rear side.
The conventional connector with a built-in circuit element shown in FIGS. 7-9 has a problem, however, that the leads 161 and 162 may be damaged or otherwise broken when the connector is used in a high-temperature environment. This problem will be discussed below in greater detail with reference to FIG. 7.
In a high-temperature environment, the resin connector case 100 undergoes thermal expansion. In this instance, a temperature-dependent dimensional change occurring at the lateral distance L between the element-connecting terminals 132 and 152 fixed to the connector case 100 is approximately equal to the product of a coefficient of thermal expansion of the connector case 100 and the lateral distance L. On the other hand, the leads 161 and 162 are made of metal and have a smaller coefficient of thermal expansion than the resin connector case 100. Thus, due to the difference in thermal expansion, the metal leads 161, 162 soldered to the element-connecting terminals 132, 52 are subjected to a tensile force and, hence, a lateral stress is developed in each of the soldered joint portions between the leads 161, 162 and the element-connecting terminals 132, 152. In the event that the lateral stress occurs repeatedly, the soldered joint portions will cause a fatigue breakdown. Since the vehicle engine room temperature shows a tendency to increase, the connector with a built-in circuit element for use in a vehicular AC generator installed in the engine room is required to solve the foregoing problem.
Japanese Patent Laid-open Publication (JP-A) No. 10-318403 (corresponding to U.S. Pat. No. 6,033,189) shows a prior proposal for preventing a fatigue breakdown from occurring, wherein the leads of a leaded circuit element have a bent portion to absorb a displacement caused due to temperature variations. The prior proposal is, however, directed to a control valve for compressors, which has a resin molded structure in its entirety with a circuit element integrally molded with a body of the resin molded control valve. If this structure is employed in a vehicular AC generator, since the vehicular AC generator per se forms a high-temperature heat source as compared to the compressor, the circuit element and its peripheral portion will be subjected to a great thermal stress, tending to form a crack at interface boundary between the molded resin and the circuit element or between the molded resin and the leads of the circuit element. Additionally, since the vehicular AC generator is placed in a use environment with high risk of getting wet with water, water entering the crack may cause an insulation failure or short between the leads of the circuit element or the circuit element itself, resulting in malfunction of the AC generator.